Adult T cell leukemia-lymphoma (ATL) is a rare but aggressive form of T cell malignancy, which is caused by human T celll leukemia virus or HTLV-I. HTLV-I is transmitted through sexual contacts, blood transfusion, sharing of contaminated needles and possibly through insect vectors as well. The Caribbean basin is one of very few "HOT SPOTS" in the world where clustering of ATL and HTLV-I infection has been noted. It has been suggested that intravenous drug addicts among whom HTLV-I is highly prevalent, are quite often double-infected by HTLV-I and human immunodeficiency virus (HIV or HTLV-III); and also that endemic HTLV-I infection might be the triggering factor for aggravated HIV infection and AIDS development among these individuals. Wide spread i.v. drug addiction is a serious health as well as socioeconomic problem in Puerto Rico, and the incidence of AIDS on the island is extremely high, indeed. It is, therefore, quite probable that an endemic HTLV-I infection among the drug addict population, should it exist, contributed to an increase of HIV infection and AIDS development here as well. In spite of the magnitude of the problem in Puerto Rico, there is no datum available presently indicating the prevalence of either HTLV-I infection or ATL in this island. The present study proposes to initiate investigation to determine; (i) the prevalence of ATL and/or HTLV-I infection in Puerto Rico. (ii) How HTLV-I infection among drug addict population affects their susceptibility to HIV infection and AIDS development, prospectively. The study will be conducted by instituting an immunophenotyping program of lymphoma-leukemia and through seroepidemiological approaches. The human subject groups to be included in the study are; (a) normal healthy blood donors; (b) self admitted i.v. drug addicts; (c) close friends, family members and relatives of (b); (d) AIDS and ARC patients and HIV seropositive individuals; (e) close friends, family members and relatives of (d); (f) non-Hodgkin's lymphoma-leukemia patients; (g) close friends, family members and relatives of (f).